This invention relates to a fluid flow device, such as a vacuum pump, blower, or compressor, and, more particularly to such a device having an improved system for cooling the device during operation.
Positive displacement fluid flow devices, such as vacuum pumps, blowers, and compressors are well know and provide certain advantages over other types of units such as fan-type blowers, turbine pumps and reciprocating pumps. For example, the positive displacement devices have no valves, pistons or other reciprocating mechanical parts. Also, they enjoy a relatively high volumetric capacity and operate with little or no backflow. As a result, they are relatively simple in construction and operation, yet are relatively rugged and reliable.
A typical positive displacement fluid flow device of the above type utilizes one or more impellers that are rotatably mounted in a chamber formed in a casing, or housing. An outer surface of each impeller extends with minimal clearance relative to the corresponding inner wall portion of the casing defining the chamber. Fluid to be processed, such as air, is introduced into an inlet at one end of the casing, and is trapped between the impellers and the casing, producing a vacuum which moves the gas to an outlet at the other end of the casing.
In some of these designs, a jet plenum is provided in the casing through which atmospheric air flows into the space between the lobes of the impellers and the casing during operation. This cools the trapped fluid, aids impeller movement, and reduces shock and power loss.
However there are problems associated with these types of designs. For example, the cooling air is often supplied through a manifold bolted to the casing on the discharge side thereof. However, the bolted manifold is bulky and takes up considerable space. Also, the discharge side of the casing is hot and thus heats the manifold and therefore the cooling air, which reduces its efficiency. Further, since the pressure of the fluid being processed is greater at the outlet than that at the inlet, there can be a blackflow of the relative hot fluid from the outlet back into the chamber and into the jet plenum for the cooling air. This, of course, also heats the cooling air and reduces its efficiency.
Therefore, what is needed is a positive displacement fluid flow device of the above type which minimizes any pre-heating of the cooling air and avoids the problems associated with a bolt-on manifold.